1. Field of the Invention
The present invention relates to a novel physiologically active peptide and salts thereof, and to antiallergic agents containing the same as an active ingredient. Furthermore, it is concerned with a method for the prevention or therapy of allergies.
2. Description of Prior Art
A variety of drugs have been proposed and developed for the prevention or therapy of various allergic diseases. Some of them have already been placed on the market.
Among the allergic symptoms, immediate-type allergic reactions such as bronchial asthma, urticaria and allergic rhinitis are classified as type I-allergic reaction. The type I-allergic reaction is in general believed on the basis of onset of the symptoms and action mechanism of the antiallergic agent to involve the following three stages: against an extraneous antigen which has entered the body produces IgE antibody, which is fixed to the Fc receptor in tissue mast cells or blood basophils thereby producing sensitization (this process is at the first stage); next, when the extraneous antigen again enters the body, the IgE antibody fixed to the Fc receptor in the cells and the extraneous antigen are bonded to cause antigen-antibody reaction which triggers such reactions as activation of the cell membrane enzymes and inflow of calcium ions into cells thereby producing biochemical changes such as enzymatic reactions and histological changes such as degranulation with a result that chemical mediators such as histamine and SRS-A are released outside the cells (this process is at the second stage); the chemical mediators released outside the cells as mentioned above have such actions as contraction of smooth muscles and accentuation of permeability and promotion of excretion of the capillary blood vessels and cause various allergic symptoms (this process is at the third stage).
Among heretofore known antiallergic agents, nonspecific hyposensitization therapeutic agents and antibody production inhibitory agents are drugs acting on the first stage. None of the drugs specifically acting on the first stage has been placed on the market. As drugs acting on the second stage are known chemical mediator-inhibitory agents such as disodium cromoglycate (DSCG) and Tranilast. Antihistaminics and bronchodilators are drugs acting on the third stage. Japanse Patent Publication Sho No. 60-2318 discloses peptide antiallergic agents though not placed on the market. Whereas the peptide has not yet been demonstrated for inhibition of the IgE antibody production at the first stage, it blocks allergic reaction by inhibiting bond of the IgE antibody with mast cells which first occurs at the second stage, as well as by simultaneously substituting the IgE antibody already bonded at the second stage. It is composed of five amino acid residues in Fc region of IgE antibody and, as shown below by the primary structure, is a pentapeptide of IgE antibody origin. EQU Asp-Ser-Asp-Pro-Arg
Although the peptide is under investigation and development as a pharmaceutical preparation, its level of the activity is not clear.
Based on the mechanism of the onset of allergic symptoms in the type I-allergic reaction, development of antiallergic agents has heretofore been directed to a drug acting on one of the three stages for the onset of allergic symptoms. Studies were made of prevention of onset or therapeutic treatment of allergic symptoms by blocking at any one stage in the chain of the three stages. Therapy which is expected to produce some efficacy has been developed by the development of drugs acting on one of the three stages in the onset of allergic symptoms.
These chemotherapeutic agents, however, cannot completely block the chain of the above-mentioned three stages. Thus, use of a combination of several drugs has been adopted based on an idea of realizing complete blocking of the chain by combined use of a drug acting on one of the three stages with a drug acting on another, but the results are not as expected.
Then, it is expected that development of a drug acting on plural stages of the three stages in the onset of allergic symptoms would drastically improve the effects as an antiallergic agent, and development of such drugs is desirable.
It is also conceivable on the basis of mechanism of the onset of allergic symptoms that superior antiallergic agents would become available if a peptide of IgE antibody origin or a peptide analogous to such peptide is developed. Development of novel peptides by the above-mentioned approach is also expected.